Home » Pluto Day : Pluto the Dwarf Planet

Pluto Day : Pluto the Dwarf Planet

Pluto was first discovered on the 18th February 1930 by astronomer Clyde William Tombaugh. It was considered the ninth planet till 2006, when the International Astronomical Union declared Pluto as a dwarf planet as it does not meet all the requirements of a full size planet.

Pluto is described as a complex world of ice mountains and frozen plains by NASA. Smaller than Earth’s Moon in size, Pluto has 5 spinning Moons. Being only 2,380 km wide, Pluto is about half the width of the United States. It is 5.5x smaller than Earth.

One of the most fascinating things about this dwarf planet is the snow. The latter is red instead of being white as we normally know here on earth. This is due to the chemical composition of the thin atmosphere on Pluto, which consists of nitrogen, methane and carbon dioxide.

Pluto @NASA

Found on the edge of our solar system, in a region called the Kuiper Belt, Pluto orbits the Sun about 5.8 billion km away on average, which is about 40 times as far as the Earth. Being that far, the surface of Pluto is way too cold to be inhabited. The temperature is about -228 to -238 C. A year on Pluto is 248 Earth years. A day on Pluto lasts 153 hours.

On February 18, 1930, Pluto was discovered by Clyde William Tombaugh at the Lowell Observatory in Arizona. Reports suggest that this discovery was the fruit of a new astronomical technique of photographic plates combined with a blink microscope. 

The name Pluto was given by an 11 year old girl, Venetia Burney from England. It was inspired by the Roman God of the underworld. Pluto’s five moons, Styx, Charon, Nix, Hydra and Kerberos, were also named after mythological figures from the underworld. 

” Pluto is the name of the Roman god of the Underworld, equivalent to the Greek Hades. However, the Greek name “Plouton” (from which the Romans derived their name “Pluto”) was also occasionally used as an alternative name for Hades. But Pluto is definitely the Roman spelling. ” Dr. Elizabeth Vandiver, chair of the Department of Classics in Whitman College in Walla Walla, Washington.

Styx is the mythological river that separates the world of living from the realm of the dead. Charon is the boatman who ferries souls to the underworld. Nix, the mother of Charon, is the goddess of darkness and night. Hydra is the nine headed serpent that guards the underworld. And Kerberos is the three headed dog of Greek mythology.

Till now only one spacecraft has visited Pluto. On July 14, 2015, NASA’s New Horizons spacecraft made its historic flight through the Pluto system. From this unique expedition, NASA obtained the first close up images of Pluto and its moons. They also derived new data that changed the knowledge of the unknown and mysterious worlds. This discovery is described as the one of the most enchanting ever made. “ It’s clear to me that the solar system saved the best for last ! ” said Alan Stern, New Horizons principal investigator from the Southwest Research Institute, Boulder, Colorado. “ We could not have explored a more fascinating or scientifically important planet at the edge of our solar system. The New Horizons team worked for 15 years to plan and execute this flyby and Pluto paid us back in spades! ”

As bewitching as it is, Pluto is unfortunately not considered as a planet since 2006. The International Astronomical Union (IAU) downgraded the status of Pluto to that of  “dwarf planet” as it does not meet the required criteria. There are 3 criteria to be considered as a full size Planet and Pluto only meets two of them. First, the Planet must orbit around the sun. Second, the planet must have sufficient mass to assume hydrostatic equilibrium (a nearly round shape). And third, the planet must clear the neighborhood around its orbit. Even though Pluto has lived there for billions years, it has failed to respect the last one. Being not able to clear its neighboring region of other objects means that the planet has become gravitationally dominant. There are no other bodies of comparable size other than its own satellites or those otherwise under its gravitational influence, in its vicinity in space.

There are 13 planets in our solar system among which only 8 are considered as full size planets. They are classified into three categories, Terrestrial planets, Gas Giants and Ice Giants. Mercury, Venus, Earth and Mars are terrestrial planets. Jupiter and Saturn are the gas giants. Uranus and Neptune are the ice giants.

Pluto is not the only dwarf planet. There are 4 more dwarf planets namely, Eris, Haumea, Makemake and Ceres. As a tribute to Pluto for being demoted, dwarf planets are also called Plutoids.